The Microsynodontis (Teleostei: Siluriformes: Mochokidae) of the lower Guinea region, west central Africa, with the description of eight new species
Author
Ng, Heok Hee
text
Zootaxa
2004
531
1
52
journal article
10.5281/zenodo.157924
9e7e41e3-cc57-40b7-8305-659cae0868a8
11755326
157924
Microsynodontis emarginatus
sp. nov.
(
Fig. 8
)
Type
material.
Holotype
: CU 89393, male,
33.4 mm
SL
;
Gabon
: HautOgooué Province, Motobo I village, Kiéne creek,
1°32'14.1"S
13°32'43.5"E
; J. P. Sullivan et al.,
12 August 1999
.
Paratypes
. CU 80567 (29),
8 females
:
26.1–30.8 mm
SL
;
20 males
:
23.4–33.6 mm
SL
; 1 unsexed:
19.5 mm
SL
; data as for
holotype
.
Diagnosis.
Microsynodontis emarginatus
can be distinguished from all congeners in having an emarginate (vs. rounded or truncate) caudal fin (
Fig. 9
). It also exhibits no noticeable sexual dimorphism in the size and density of the tubercles on the dorsal and lateral surfaces of the head, unlike all other lower
Guinea
species of
Microsynodontis
.
Description.
Biometric and meristic data as in
Table 3
. Body compressed. Predorsal profile gently convex; postdorsal body sloping gently ventrally. Preanal profile horizontal. Anus and urogenital openings located at vertical through middle of pelvic fin. Skin smooth. Lateral line complete and midlateral.
Head depressed and broad, broadly rounded when viewed laterally and with rounded snout margin when viewed from above. Gill openings narrow, extending from immediately ventral to posttemporal to immediately ventral to base of pectoral spine. Gill membranes united to, and attached across, isthmus. Bony elements of dorsal surface of head covered with thin skin. Nuchal shield large and terminating posteriorly with two rounded processes on each side. Supracleithral process thin, extending just short of vertical through posteriormost tip of nuchal shield.
FIGURE 8.
Microsynodontis emarginatus
, holotype, CU 89393, 33.4 mm SL; Gabon: Ogooué River drainage.
TABLE 3
. Biometric data for
M. emarginatus
(n=30).
| HOLOTYPE |
RANGE |
MEAN±SD |
| SL (mm) |
33.4 |
19.5–33.6 |
| In % SL |
| Predorsal length |
35.3 |
35.3–39.9 |
36.6±1.49 |
| Snout to anal |
68.8 |
66.5–71.9 |
68.7±1.74 |
| Snout to pelvic |
51.6 |
48.2–52.6 |
50.7±1.59 |
| Snout to pectoral |
20.3 |
19.9–24.7 |
22.4±1.63 |
| Dorsalfin base length |
14.7 |
13.6–16.5 |
14.8±0.87 |
| Dorsal spine length |
17.2 |
16.8–19.9 |
18.0±1.25 |
| Analfin base length |
12.5 |
10.5–14.6 |
12.8±1.44 |
| Pelvicfin length |
13.8 |
13.8–15.9 |
14.8±0.67 |
| Pectoral fin length |
24.1 |
21.6–25.1 |
23.3±1.22 |
| Pectoral spine length |
22.5 |
19.2–22.8 |
20.9±1.45 |
| Caudal total length |
22.5 |
21.4–25.8 |
23.7±1.64 |
| Adipose basal length |
28.1 |
27.9–30.2 |
28.7±0.79 |
| Adipose maximum height |
4.1 |
4.4–5.5 |
5.1±0.94 |
| Dorsal to adipose distance |
18.4 |
11.8–18.4 |
15.2±1.97 |
| Adipose to caudal peduncle |
8.4 |
8.4–12.5 |
10.3±1.35 |
| Caudal peduncle length |
16.3 |
16.1–19.3 |
17.7±1.31 |
| Caudal peduncle depth |
8.8 |
8.4–9.8 |
8.8±0.44 |
| Body depth at anus |
14.7 |
14.0–16.9 |
15.2±0.94 |
| Head length |
27.2 |
25.0–28.2 |
27.2±1.02 |
| Head width |
21.9 |
21.9–25.2 |
24.0±1.06 |
| Head depth |
16.9 |
16.2–19.2 |
17.5±0.93 |
| In % HL |
| Snout length |
42.5 |
41.4–47.9 |
44.8±2.59 |
| Interorbital distance |
36.8 |
34.0–41.2 |
37.0±2.24 |
| Orbit diameter |
21.8 |
17.8–21.2 |
19.2±1.04 |
| Maxillary barbel length |
98.9 |
91.8–109.5 |
102.8±6.92 |
| Inner mandibular barbel length |
55.2 |
44.1–59.5 |
55.4±5.01 |
| Outer mandibular barbel length |
74.7 |
68.8–85.3 |
75.5±5.21 |
Barbels in three pairs. Maxillary barbel long and slender, extending to just beyond base of last pectoralfin ray. Inner mandibularbarbel origin close to midline, extending to base of pectoral spine and with 2 short, thin branches on anterior half and 3–5 long, thin branches on posterior half. Outer mandibular barbel originates posterolateral of inner mandibular barbel, extending to middle of pectoralfin base and with 3–5 long, thin branches.
FIGURE 9.
Lateral view of caudal fins showing: a. emarginate fin (condition in
Microsynodontis emarginatus
, CU 89393, holotype, 33.4 mm SL); b. rounded fin (other
Microsynodontis
species, represented by
M. batesii
, CU 80748, 33.2 mm SL); c. truncate fin (condition in
M. laevigatus
and
M. lamberti
, represented by
M. laevigatus
, CU 88265, paratype, 22.8 mm SL).
Eye ovoid, horizontal axis longest; located entirely in dorsal half of head. Orbit without free margin.
Mouth inferior and crescentshaped; lips plicate. Oral teeth in rows on all toothbearing surfaces. Premaxillae narrow, with narrow ventral shelf and partially exposed when mouth closed. Primary teeth 9–11, conical and separated from secondary teeth by distinct gap. Secondary teeth 35–50, acutely pointed and recurved; disposed in 3–4 rows. Tertiary teeth 15–24, elongate, villiform and extending over full width of premaxillae. Dentary teeth 15–21, acutely pointed, strongly recurved and broader than secondary teeth; disposed in one or two transverse bands.
Dorsal fin located at anterior third of body, with II,7 (30) rays and convex margin. Dorsalfin spine long, stout and slightly curved; smooth on both anterior and posterior margins. Adipose fin moderately long; margin slightly convex for entire length and posterior end deeply incised. Caudal fin emarginate (
Fig. 10
a), with i,6,5,i (3) or i,6,6,i* (27) principal rays. Procurrent rays symmetrical and extend only slightly anterior to fin base. Analfin base located ventral to posterior half of adipose fin. Anal fin with iv,6 (1); iv,7* (22) or iv,8 (7) rays and convex margin. Pelvicfin origin at vertical ventral to posterior end of dorsalfin base. Pelvic fin with i,6 (30) rays and slightly convex margin; tip of appressed fin not reaching analfin origin. Pectoral fin with I,6 (30) rays; spine slightly curved and stout (
Fig. 4
c). Anterior spine margin with 15–22 small serrations along entire length of spine; serrations antrorse (distally directed) on distal two thirds and anteriorly directed on proximal third. Posterior spine margin with 7–9 strong serrations along entire length. Pectoralfin margin convex posteriorly. Vertebrae 13+22=35 (1); 12+24=36 (3); 13+23=36* (18); 13+24=37 (6); 14+22=36 (1) or 14+23=37 (1).
No marked sexual dimorphism in the size and density of tubercles on head. Males with long genital papilla situated immediately posterior to anus. Females with smaller, distally flattened genital papilla.
Coloration.
In 70% ethanol: dorsal and lateral surfaces and of head and body medium brown, fading to cream or light grayish brown on ventral third of body, belly (with large faint brown spots), and ventral surface of head (
Fig. 8
). Snout with a series of cream spots delineating anterior and posterior nares, sometimes coalescing to form cream band running from anterior orbital margin to tip of snout. Cheek region with one or two cream spots immediately ventral to orbit. Cream band encircling nape at supraoccipital. Dorsal third of body with series of four cream vertical barshaped marks extending beyond lateral midline of body: first at middle of dorsalfin base, second at adiposefin origin, third at middle of adiposefin base and last on caudal peduncle immediately posterior to adipose fin, sometimes encircling caudal peduncle as cream band. Ventral third of flanks with a longitudinal series of five to seven cream spots or vertical barshaped marks. Dorsal, pectoral, pelvic and anal fins hyaline and sometimes with one to two rows of faint spots forming longitudinal brown rows. Caudal fin with similar series of elongate marks forming two to three irregular columns.
Distribution.
Known from the upper Ogooué River in southeastern
Gabon
(
Fig. 7
).
Habitat.
The
type
locality is a very slowflowing creek. Water temperature was 25.4°C and the
pH
was 5.0. Syntopic fish included:
Mormyridae
:
Brienomyrus
spp.,
Marcusenius moorii
,
Mormyrops zanclirostris
,
Stomatorhinus walkeri
;
Characidae
:
Brycinus
sp.;
Distichodontidae
:
Distichodus
sp.,
Nannocharax
sp.;
Hepsetidae
:
Hepsetus odoe
;
Cyprinidae
:
Barbus
spp.;
Amphiliidae
:
Amphilius nigricaudatus
,
Phractura
sp.,
Clariidae
:
Clarias
spp.;
Claroteidae
:
Parauchenoglanis balayi
;
Mochokidae
:
Synodontis
sp.;
Cyprinodontidae
:
Plataplochilus terveri
;
Channidae
:
Parachanna insignis
;
Cichlidae
:
Hemichromis
sp.;
Anabantidae
:
Ctenopoma kingsleyae
;
Mastacembelidae
:
Caecomastacembelus
sp.
Etymology.
From the Latin
emarginatus
, meaning notched at the apex; in reference to distinctive shape of the caudal fin. Used as an adjective.